It is widely known that knowing the position and speed of the vehicles on the road network in real-time is one of the major challenges that vehicle control and traffic management applications are facing [2]. Wireless Sensor Network (WSN) is considered as a potential technology that might be useful as an infrastructure component of an ITS since it received significant attention in the last decade and successful research put them in the forefront to answer this challenge [2].

A wireless sensor network is a collection of nodes organized into a cooperative network. Each node consists of processing capability (one or more microcontrollers, CPUs or DSP chips), may contain multiple types of memory (program, data and flash memories), have a RF transceiver (usually with a single omni-directional antenna), have a power source (e.g., batteries, solar cells), and accommodate various sensors and actuators. The nodes communicate wirelessly and often self-organize after being deployed in an ad hoc fashion [1]. It is an infrastructure comprised of sensing(measuring), computing, and communication elements that gives the user the ability to instrument, observe, and react to events and phenomena in specified environment. The environment can be the physical world, or a biological system [3].

Currently, wireless sensor networks are beginning to be deployed at an accelerated pace. It is not unreasonable to expect that in 10-15 years that the world will be covered with wireless sensor networks with access to them via the Internet. This can be considered as the Internet becoming a physical network. This new technology is exciting with unlimited potential for numerous application areas including environmental, medical, military, transportation, entertainment, crisis management, homeland defense, and smart spaces [1].

Some typical applications of Wireless Sensor Network are tracking, monitoring, and controlling. In a typical application, a WSN is scattered in a region where it is meant to collect data through its sensor nodes. Existing and potential applications of sensor networks include, among others, military sensing, physical security, air traffic control, traffic surveillance, video surveillance, industrial and manufacturing automation, process control, inventory management, distributed robotics, weather sensing, environment monitoring, national border monitoring, and building and structures monitoring [3].

Key Technology

The basic functionalities for WSN depends on the application, which in this case is ITS. There are several type of sensor parameters, including: physical measurements, chemical and biological measurements, and event measurements. In ITS, the most important features are the vehicle states, which includes position, speed, direction. Other possibility of feature is classification, for example: is a vehicle in traffic a car, a truck, or a bus? Some possible sensors for ITS includes magnetoresistive, light, pressure, and video (visible or infrared).

As for the transmission part, there are several wireless transmission technologies available. WSN can use some wireless technologies such as Bluetooth, ZigBee, Wireless LAN, WiMax, and 3G. The requirements of communication are related to the implementation of ITS. Some properties that have to be put into considerations are: range of communication, data throughput, and power consumption. In term of range, 3G covers the longest range, continue by WiMax, Wireless LAN, Bluetooth and Zigbee. Theoretically all those technologies are useful for ITS, however it is all depend on the topology and implementation of the system.

ITS typically does not involved a high data rate communication, however if the system requires a responsive, real-time communication then using ZigBee is arguably not very suitable since it data rates is as low as 20 kbps. However, it is designed to run several years on a single set of batteries [3]. Bluetooth offers approximately 1 to 3 Mbps and Wireless LAN have a maximum data transmission rate of 54 Mbps, but none of them as energy-efficient as ZigBee.

Each sensor node needs an operating system which capable of controlling hardware, provides hardware abstraction, and fill in the gap between application and hardware. TinyOS is one of the de facto standards of operating system designed specifically for WSN. It component library includes network protocols, distributed services, sensor drivers, and data acquisition tools. TinyOS’s event-driven execution model enables fine-grained power management, yet allows the scheduling flexibility made necessary by the unpredictable nature of wireless communication and physical world interfaces [3]. Some of its advantages are [3]:

It requires very little code and a small amount of data

Events are propagated quickly and the rate of posting a task and switching the corresponding context is very high

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